ERBB2 and breast cancer: Human breast cancer is a heterogeneous disease that can be segregated into at least six distinct subtypes based on gene expression profiles: basal-like, claudin-low, human epidermal growth factor receptor 2 (HER2)-enriched, luminal A, luminal B and normal-like (Perou et al., 2000; Prat et al., 2010; Cancer Genome Atlas Network, 2012).